The impact of sickle cell trait on glycated haemoglobin in diabetes mellitus

Global variation in diabetes diagnosis and prevalence based on fasting glucose and hemoglobin A1c

Fasting plasma glucose (FPG) and hemoglobin A1c (HbA1c) are both used to diagnose diabetes, but these measurements can identify different people as having diabetes. We used data from 117 population-based studies and quantified, in different world regions, the prevalence of diagnosed diabetes, and whether those who were previously undiagnosed and detected as having diabetes in survey screening, had elevated FPG, HbA1c or both. We developed prediction equations for estimating the probability that a person without previously diagnosed diabetes, and at a specific level of FPG, had elevated HbA1c, and vice versa. The age-standardized proportion of diabetes that was previously undiagnosed and detected in survey screening ranged from 30% in the high-income western region to 66% in south Asia. Among those with screen-detected diabetes with either test, the age-standardized proportion who had elevated levels of both FPG and HbA1c was 29-39% across regions; the remainder had discordant elevation of FPG or HbA1c. In most low- and middle-income regions, isolated elevated HbA1c was more common than isolated elevated FPG. In these regions, the use of FPG alone may delay diabetes diagnosis and underestimate diabetes prevalence. Our prediction equations help allocate finite resources for measuring HbA1c to reduce the global shortfall in diabetes diagnosis and surveillance.

HbA1c Performance in African Descent Populations in the United States With Normal Glucose Tolerance, Prediabetes, or Diabetes: A Scoping Review

INTRODUCTION

African descent populations in the United States have high rates of type 2 diabetes and are incorrectly represented as a single group. Current glycated hemoglobin A1c (HbA1c) cutoffs (5.7% to <6.5% for prediabetes; ≥6.5% for type 2 diabetes) may perform suboptimally in evaluating glycemic status among African descent groups. We conducted a scoping review of US-based evidence documenting HbA1c performance to assess glycemic status among African American, Afro-Caribbean, and African people.

METHODS

A PubMed, Scopus, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) search (January 2020) yielded 3,238 articles published from January 2000 through January 2020. After review of titles, abstracts, and full texts, 12 met our criteria. HbA1c results were compared with other ethnic groups or validated against the oral glucose tolerance test (OGTT), fasting plasma glucose (FPG), or previous diagnosis. We classified study results by the risk of false positives and risk of false negatives in assessing glycemic status.

RESULTS

In 5 studies of African American people, the HbA1c test increased risk of false positives compared with White populations, regardless of glycemic status. Three studies of African Americans found that HbA1c of 5.7% to less than 6.5% or HbA1c of 6.5% or higher generally increased risk of overdiagnosis compared with OGTT or previous diagnosis. In one study of Afro-Caribbean people, HbA1c of 6.5% or higher detected fewer type 2 diabetes cases because of a greater risk of false negatives. Compared with OGTT, HbA1c tests in 4 studies of Africans found that HbA1c of 5.7% to less than 6.5% or HbA1c of 6.5% or higher leads to underdiagnosis.

CONCLUSION

HbA1c criteria inadequately characterizes glycemic status among heterogeneous African descent populations. Research is needed to determine optimal HbA1c cutoffs or other test strategies that account for risk profiles unique to African American, Afro-Caribbean, and African people living in the United States.

Influence of hemoglobinopathies and glucose-6-phosphate dehydrogenase deficiency on diagnosis of diabetes by HbA1c among Tanzanian adults with and without HIV: A cross-sectional study

INTRODUCTION

Hemoglobin A1c (HbA1c) is recommended for diagnosing and monitoring diabetes. However, in people with sickle cell disease (SCD), sickle cell trait (SCT), α-thalassemia or glucose-6-phosphate dehydrogenase (G6PD) deficiency, HbA1c may underestimate the prevalence of diabetes. There are no data on the extent of this problem in sub-Saharan Africa despite having high prevalence of these red blood cell disorders.

METHODS

Blood samples from 431 adults in northwestern Tanzania, randomly selected from the prospective cohort study, Chronic Infections, Comorbidities and Diabetes in Africa (CICADA), were analysed for SCT/SCD, α-thalassemia and G6PD deficiency and tested for associations with the combined prevalence of prediabetes and diabetes (PD/DM) by HbA1c, using the HemoCue 501 HbA1c instrument, and by 2-hour oral glucose tolerance test (OGTT).

RESULTS

The mean age of the participants was 40.5 (SD11.6) years; 61% were females and 71% were HIV-infected. Among 431 participants, 110 (25.5%) had SCT and none had SCD. Heterozygous α-thalassemia (heterozygous α+ AT) was present in 186 (43%) of the participants, while 52 participants (12%) had homozygous α-thalassemia (homozygous α+ AT). Furthermore, 40 (9.3%) participants, all females, had heterozygous G6PD deficiency while 24 (5.6%) males and 4 (0.9%) females had hemizygous and homozygous G6PD deficiency, respectively. In adjusted analysis, participants with SCT were 85% less likely to be diagnosed with PD/DM by HbA1c compared to those without SCT (OR = 0.15, 95% CI: 0.08, 0.26, P < 0.001). When using OGTT, in adjusted analysis, SCT was not associated with diagnosis of PD/DM while participants with homozygous α+ AT and hemizygous G6PD deficiency were more likely to be diagnosed with PD/DM.

CONCLUSIONS

HbA1c underestimates the prevalence of PD/DM among Tanzanian adults with SCT. Further research using other HbA1c instruments is needed to optimize HbA1c use among populations with high prevalence of hemoglobinopathies or G6PD deficiency.

The Sickle Effect: The Silent Titan Affecting Glycated Hemoglobin Reliability

Hemoglobin A1c (HbA1c) is a popular invaluable tool in the diagnosis of Type 2 diabetes for red blood cells (RBCs) with a lifespan of 120 days; however, many factors, including hemoglobinopathies, affect its accuracy. Sickle cell trait, primarily a benign medical condition, is a point mutation in only one of two beta-globin genes on chromosome 11. We performed a traditional review to identify how the sickle cell trait (SCT) affects the interpretation of HbA1c and the further implications it may have on the diagnosis and management of Type 2 diabetes. A literature search was performed using PubMed®/MEDLINE® and Google Scholar with formulated keywords (sickle cell trait, HbAS, HbA1c, glycosylated hemoglobin, diabetes, RBC lifespan, race, and genetics), with the majority of results being mainly observational studies. The National Glycohemoglobin Standardization Program (NGSP) is responsible for standardizing HbA1c results and also highlights factors that can interfere with HbA1c, including hemoglobin variants. Studies that utilize only an NGSP-certified method with no clinically significant interference by HbS in patients with and without SCT showed contrasting results. Additional studies showed that persons of African ancestry, the group to which the majority of SCT patients belong, have a higher HbA1c than non-Hispanic whites (NHWs), just based on race, and a greater probability of having glucose-6-phosphate dehydrogenase (G6PD) deficiency, which lowers HbA1c. The most extensive study investigating the RBC lifespan in SCT patients showed a reduction in the cell lifespan compared to normal patients; however, other smaller studies were contradictory. Our study highlights the need for hemoglobinopathy detection before or during HbA1c measurement in populations with a high degree of African ancestry and the importance of patient notification. It also shows that SCT affects the accuracy of HbA1c, through its likely reduction of RBC lifespan and its increased association with African ancestry and G6PD deficiency. This review recommends that for SCT patients with potential Type 2 diabetes, HbA1c should be used in combination with another diagnostic tool such as fasting blood glucose, fructosamine, or glycated albumin to decrease the chances of a missed diagnosis.

Fasting glucose-to-HbA1c ratio is a good indicator of G6PD deficiency, but not thalassemia, in patients with type 2 diabetes mellitus

AIMS

Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency or thalassemia have a shorter red blood cell lifespan; therefore, HbA1c is underestimated in these patients. To address these issues, we sought an early indicator for G6PD deficiency or thalassemia in DM patients.

METHODS

A total of 4908 patients with DM and 1848 subjects without DM were included in this study. Fasting glucose (FG) levels, HbA1c levels, hemogram profiles and G6PD activities were measured. Genotypic analyses of G6PD deficiency and thalassemia were performed.

RESULTS

DM patients with G6PD deficiency had significantly higher FG/HbA1c ratios than did those without G6PD deficiency (26.54 vs. 18.36; p < 0.0001). We divided the FG level into four categories: ≤150, 151-250, 251-350, and ≥351 mg/dL. Among all groups, only patients with DM and G6PD deficiency had higher FG/HbA1c ratios than those of patients with DM alone or DM with thalassemia. To evaluate the reliability of the FG/HbA1c ratio, receiver operating characteristic analyses were performed. The areas under the curve for detecting FG ≤ 150, 151-250, 251-350, and ≥351 mg/dL with G6PD deficiency based on the FG/HbA1c ratio were 0.839 (p < 0.001), 0.888 (p < 0.001), 0.891 (p < 0.001), and 0.640 (p = 0.3954), respectively. G6PD deficiency was confirmed by genetic analysis. We found common mutations that influenced G6PD activity and HbA1c levels.

CONCLUSIONS

The FG/HbA1c ratio is a good indicator of DM with G6PD deficiency. If this ratio is determined to be high in a clinical setting, then the clinician must consider whether the patient has a G6PD deficiency, and HbA1c reference values must be adjusted to avoid misdiagnosis and incorrect treatment decisions.

A labile form of hemoglobin A1c is higher in African-American youth with type 1 diabetes compared to Caucasian patients at similar glucose levels

BACKGROUND

Hemoglobin A1c (HbA1c) levels are higher in African-American (AA) individuals compared to Caucasians (EA) even after adjustment for blood glucose levels. To better understand the mechanism of this disparity we examined the relationship of an unstable (labile) form of HbA1c (L-HbA1c) with race and glucose.

METHODS

Samples for HbA1c were collected from pediatric patients self-identified as either AA (15F, 12M, age 13.4 ± 3.5 years) or EA (22F, 30M, age 14.6 ± 3.4 years) with type 1 diabetes at the time of a clinic visit. Clinic HbA1c (HbA1c) was performed by immunoassay. L-HbA1c equaled the difference in the HbA1c fraction by dynamic capillary isoelectric focusing before and after incubation in a low pH buffer. A capillary glucose (Clinic-BG) was measured at clinic visit. Mean blood glucose (MBG) was calculated from the last 30 days of the patient's glucose meter data. The influence of race on L-HbA1c was assessed in a multiple variable regression model adjusted for Clinic-BG.

RESULTS

The groups were similar for age and duration of diabetes. L-HbA1c was correlated with Clinic-BG, MBG, and HbA1c. The mean levels of L-HbA1c, HbA1c, MBG, but not Clinic-BG were higher in AA patients compared to EA. After adjustment for Clinic-BG, L-HbA1c was still higher in AA (2.8 ± 0.7% AA vs 2.1 ± 0.7% EA, P < .0001).

CONCLUSIONS

L-HbA1c is correlated with Clinic-BG. At any given level of Clinic-BG, AA patients have higher levels of L-HbA1c than EA. This preliminary study suggests that early factors prior to the formation of stable HbA1c may contribute to the observed glucose-independent racial disparity.

Genetic Ancestry Markers and Difference in A1c Between African American and White in the Diabetes Prevention Program

PURPOSE

HbA1c levels are higher in blacks than non-Hispanic whites (NHWs). We investigated whether genetics could explain this difference in Diabetes Prevention Program (DPP) participants.

METHODS

We tested (i) genetic variants causing hemoglobinopathies, (ii) a genetic risk score (GRS) based on 60 variants associated with HbA1c from genome-wide association meta-analysis, and (iii) principal component (PC) factors that capture continental ancestry derived from genetic markers distributed across the genome.

RESULTS

Of 2658 eligible DPP participants, 537 (20%) self-identified as black and 1476 (56%) as NHW. Despite comparable fasting and 2-hour glucose levels, blacks had higher HbA1c (mean ± SD = 6.2 ± 0.6%) compared with NHWs (5.8 ± 0.4%; P < 0.001). In blacks, the genetic variant causing sickle cell trait was associated with higher HbA1c [β (SE) = +0.44 (0.08)%; P = 2.1 × 10-4]. The GRS was associated with HbA1c in both blacks and NHWs. Self-identified blacks were distributed along the first PC axis, as expected in mixed ancestry populations. The first PC explained 60% of the 0.4% difference in HbA1c between blacks and NHWs, whereas the sickle cell variant explained 16% and GRS explained 14%.

CONCLUSIONS

A large proportion of HbA1c difference between blacks and NHWs was associated with the first PC factor, suggesting that unidentified genetic markers influence HbA1c in blacks in addition to nongenetic factors.

Impact of Genetic Determinants of HbA1c on Type 2 Diabetes Risk and Diagnosis

PURPOSE OF REVIEW

Glycated hemoglobin (A1c) is used to diagnose type 2 diabetes and monitor glycemic control. Specific genetic variants interfere with A1c and effects/frequencies of some variants vary by ancestry. In this review, we summarize findings from large trans-ethnic meta-analyses of genome-wide association studies (GWAS) of A1c and describe some variants influencing erythrocyte biology and interfering with A1c.

RECENT FINDINGS

Recent GWAS meta-analyses have revealed 60 loci associated with A1c in multi-ethnic populations. The main A1c genetic driver in African Americans is rs1050828 (G6PD). Some identified loci are located in/near genes known as monogenic causes of erythrocytic disorders (ANK1, SPTA1) or iron disorders (TMPRSS6, HFE). Uncommon genetic variants (not revealed by GWAS) that are known to cause hemoglobinopathies may also influence A1C levels, partly by interfering with laboratory assays. Specific genetic variants that have a large impact on A1c levels may influence clinical practice, especially in individuals of African descent. Efforts to reveal novel A1c loci should focus on increasing representation of GWAS in non-European ancestries, and on using better genome-wide coverage of uncommon variants that are specific to each population.

Access to Hemoglobin A1c in Rural Africa: A Difficult Reality with Severe Consequences

Sub-Saharan Africa (SSA) continues to have the highest diabetes-related mortality rate in the world. While there exists a multitude of health system barriers driving poor diabetes control, rural facilities particularly in SSA lack access to proper monitoring of glucose and other key biologic tests. At best, most of these diabetes patients receive random blood sugar readings only on the day of their clinic visit. This approach has very limited clinical value in determining dosage adjustments for narrow therapeutic index medications such as insulin. Furthermore, access to other blood tests and physical exam tools for detecting early signs of diabetes complications is limited. We propose that routine access to hemoglobin A1c (HbA1c) testing would not only allow for close monitoring of diabetes control but also provide critical data informing the population level risk for diabetes complications. However, implementing HbA1c testing does have its own barriers at rural facilities, including high costs, refrigeration requirements, and perceived discordance between HbA1c values and mean blood glucose levels for SSA patients. Fortunately, several pilots in rural SSA have illustrated feasibility of HbA1c testing. Further political will, price reduction, and context-specific research are needed. Increasing access to HbA1c testing is a critical step to combat the high diabetes-related mortality rates in rural SSA.

Association of Sickle Cell Trait With Hemoglobin A1c in African Americans

Importance

Hemoglobin A1c (HbA1c) reflects past glucose concentrations, but this relationship may differ between those with sickle cell trait (SCT) and those without it.

Objective

To evaluate the association between SCT and HbA1c for given levels of fasting or 2-hour glucose levels among African Americans.

Design, Setting, and Participants

Retrospective cohort study using data collected from 7938 participants in 2 community-based cohorts, the Coronary Artery Risk Development in Young Adults (CARDIA) study and the Jackson Heart Study (JHS). From the CARDIA study, 2637 patients contributed a maximum of 2 visits (2005-2011); from the JHS, 5301 participants contributed a maximum of 3 visits (2000-2013). All visits were scheduled at approximately 5-year intervals. Participants without SCT data, those without any concurrent HbA1c and glucose measurements, and those with hemoglobin variants HbSS, HbCC, or HbAC were excluded. Analysis of the primary outcome was conducted using generalized estimating equations (GEE) to examine the association of SCT with HbA1c levels, controlling for fasting or 2-hour glucose measures.

Exposures

Presence of SCT.

Main Outcomes and Measures

Hemoglobin A1c stratified by the presence or absence of SCT was the primary outcome measure.

Results

The analytic sample included 4620 participants (mean age, 52.3 [SD, 11.8] years; 2835 women [61.3%]; 367 [7.9%] with SCT) with 9062 concurrent measures of fasting glucose and HbA1c levels. In unadjusted GEE analyses, for a given fasting glucose, HbA1c values were statistically significantly lower in those with (5.72%) vs those without (6.01%) SCT (mean HbA1c difference, -0.29%; 95% CI, -0.35% to -0.23%). Findings were similar in models adjusted for key risk factors and in analyses using 2001 concurrent measures of 2-hour glucose and HbA1c concentration for those with SCT (mean, 5.35%) vs those without SCT (mean, 5.65%) for a mean HbA1c difference of -0.30% (95% CI, -0.39% to -0.21%). The HbA1c difference by SCT was greater at higher fasting (P = .02 for interaction) and 2-hour (P = .03) glucose concentrations. The prevalence of prediabetes and diabetes was statistically significantly lower among participants with SCT when defined using HbA1c values (29.2% vs 48.6% for prediabetes and 3.8% vs 7.3% for diabetes in 572 observations from participants with SCT and 6877 observations from participants without SCT; P<.001 for both comparisons).

Conclusions and Relevance

Among African Americans from 2 large, well-established cohorts, participants with SCT had lower levels of HbA1c at any given concentration of fasting or 2-hour glucose compared with participants without SCT. These findings suggest that HbA1c may systematically underestimate past glycemia in black patients with SCT and may require further evaluation.

Would sickle cell trait influence the metabolic control in sub-Saharan individuals with type 2 diabetes?

AIMS

To determine the prevalence and effects of sickle cell trait on metabolic control in a Cameroonian diabetic population in a tertiary care setup.

METHODS

This was a cross-sectional study involving 73 consecutive outpatients with Type 2 diabetes recruited from the Yaounde National Diabetes and Obesity Centre. Sickle cell trait status was based on haemoglobin electrophoresis. Metabolic control was assessed by plasma glucose and HbA(1c), and comparisons made between participants with and without sickle cell trait, with adjustment for confounders through linear regressions models.

RESULTS

The prevalence of sickle cell trait was 19%, without sex difference, and comparable with figures in individuals without diabetes in this setting. Participants with diabetes and sickle cell trait were older than the non-trait participants (66 vs. 58 years, P = 0.02). Otherwise, clinical and biological profile including indicators of metabolic control were similarly distributed between trait and non-trait participants (all P >0.08). After adjustment for confounders, sickle cell trait was unrelated to fasting glucose (β = 0.02; 95% confidence interval -37.68-43.30) and HbA(1c) (β = -0.03, 95% confidence interval -1.18-0.93), and did not affect the relationship between the two markers of diabetes control (β = -0.03, 95% confidence interval -1.18-0.89).

CONCLUSIONS

Sickle cell trait was as frequent in this subgroup of patients with Type 2 diabetes as in the general population, suggesting no specific association with diabetes. It does not affect the metabolic control of diabetes. However, how this translates into long-term outcome needs to be fully elucidated in this setting, with an increasing population with both sickle cell trait and diabetes mellitus.